Beryllium (Be)-diffused sapphire has been drawing large attention from magazines and insiders in the industry. This material has been treated by a new heating method introduced by some gem heaters in Chanthaburi, Thailand, since late last year. One gemmological laboratory in Bangkok confirmed this treatment and gave warning to the industry. This material, although in small quantity, has already been in the Japanese market; however, it can be recognised by irregular inclusions (such as photo-2 to 7) and confirmed by LA-ICP-MS or LIBS.
In Japan, regulations on the expression on identification reports were revised in September 2004 and significant change and new categories were made on corundum. This revision was led by sudden appearance of Be-diffused orange/pink sapphire (padparadscha colour) after 2002 (Scarratt, 2002). No information on the material was released by the exporting country initially, and the treatment process of gdiffusing a light elementh was totally new to the industry, so that response from gemmological laboratories and the industry fell behind. Subsequent research developed theoretical investigation to some extent (Emmett, et. al., 2003, Shida, et.al., 2002; Pisutha-Arnond, et. al., 2002, etc), however, it turned out that advanced analytical techniques which are beyond the gem identification field such as SIMS or LA-ICP-MS were required to detect Be and this fact created a controversy about a whole concept of identification technique.
Be-diffused blue sapphire is becoming a new threat to gem industry since its advent on the market in Bangkok early this year. Gem Research Swiss Lab (GRS) has confirmed a Be-diffused blue sapphire in November 2005 and it reported that the number of the material was increasing from the beginning of this year. Association of Gemmological Laboratories, Japan (AGL) gives warning to each member institution as this material was, although in small quantity, found in Japan, too.
Mechanism of Colour Change by Beryllium Diffusion
@@Major colour change by Be diffusion is explained by production of yellow colour centre due to trapped hole colour centre that is caused by a divalent element beryllium replacing trivalent aluminium in corundum (Emmett, et. al., 2003). Therefore, distinction between heated and unheated or detection of Be-diffusion, especially for sapphires in yellow series, is hard to make. The major colour change by Be-diffusion is actually quite complicated, and it can be influenced by contents of other trace elements (such as Si or Ti). When [Mg2++Be2+]>[Ti4++Si4+], for instance, trapped hole is formed by Be2+ and Mg2+ to produce yellow colour, on the other hand, when [Ti4++Si4+]>[Mg2++Be2+] more electron-providing ions exist to deform the trapped hole related to Be2+ and Mg2+ so that yellow colour is not produced. In blue sapphire, cause of the colour is said to be charge transfer of Fe2+/Ti4+, however, when Be2+ is added in oxidising atmosphere Fe2+ changes to Fe3+, and Be2+ may bonds to Ti4+ before Fe2+ to follow the principle of conservation of charge. As Be2+/Ti4+ does not related to colouring of a stone, blue sapphire dramatically may fades its colour when over a certain level of Be is added.
Response to The Be-diffused Treatment in and out of the Country
The number of Be-diffused blue sapphire confirmed by GRS has reached over a hundred since the end of last year, the majority of the stones in the 5- to 10-carat range and reportedly from Sri Lanka or Madagascar (www.gemresearch.ch).
Asian Institute of Gemological Sciences (AIGS) announced that 56 pieces of blue sapphire heated in Chanthaburi were Be-diffused heat-treated stones and it reported their internal features in detail (www.aigslaboratory.com/aigsbeblue.php). Laboratory Manual Harmonization Committee (LMHC) held an emergency meeting in Bangkok on 2nd March 2006 at the behest of Gem and Jewelry Institute of Thailand (GIT). Dr. Ahmadjan was delegated to the conference to report current situation and to discuss technical response with staff of GIA, AGTA and GIT. Researchers of AIGS and professional gem heaters in Bangkok and Chanthaburi were also invited to the conference. AGTA released after the conference its identification policy that advanced tests such as LIBS should be done when a stone shows a sign of prolonged or high-temperature heating (www.agta-gtc.org). Thai Gem and Jewelry Traders Association (TGJTA),Chantaburi Gem and Jewelry Traders Association (CGA) and Gem and Jewelry Institute of Thailand (GIT) released announcement on 23rd February 2006 that they cooperate in eliminating Be-diffused blue sapphire from gem market immediately.
Gem industry in Japan was quick to examine this issue. AGL let the colour stone committee play a central role to collect information, then opinions on the identification features were exchanged and all the member institutions were informed on this issue. Japan Jewellery Association (JJA) also discussed on this matter mainly in the colour stone-pearl department in Jewel section meeting and announced the issue to its members. JJA also requests several organisations in gem industry in Thailand to provide through disclosure when handling Be-diffused blue sapphire.
What is Beryllium-Diffused Blue Sapphire?
Beryllium detected in sapphire can be speculate its occurrence by the following two, which have been subject of controversy whether it is purposely added or accidentally contained:
1)A stone is heated in the furnace that has been used for Be-diffusion treatment, or a stone is contaminated by recycling a crucible made of alumina ceramics.
The content of Be detected by LA-ICP-MS analysis on the several area of the stone is below 1ppm (relative error}0.5 ppm, ppm is a fractional weight, also can be written as ppmw) and this is presumed to have no influence on the colour. It is now required to make response to the stones containing Be not purposely and international consensus on the limitation of detection.
2)Beryllium was added deliberately during diffusion treatment aiming at colour alteration.
One professional gem heater reported at the LMHC emergency meeting held in Bangkok on the new process with Be being added artificially on purpose to alter the colour. According to the report, when heating geuda stones from Madagascar and Sri Lanka under reducing atmosphere, 5% of them deepened the colour, which were later Be diffusion treated to lighten the colour. Some of others were also Be-diffused to improve their clarity and then they may be re-heated under reducing atmosphere. This process was developed by small number of heat treatment professionals in Chanthaburi, and its detail is speculated not revealed to other treaters. Be-diffused blue sapphires confirmed by gemmological laboratories in Bangkok such as GIT or AIGS are presumed of this type.
At GAAJ Laboratory
@@GAAJ laboratory has confirmed about ten pieces of Be-diffused blue sapphire between February and May this year (photo 1). The maximum size was 7ct, but 1 to 2ct stones were dominant. Most of them were assumed from Madagascar, except one piece that seemed to be from Thailand.
LA-ICP-MS analysis detected about several ppm to several dozens ppm of Be from those Be-diffused blue sapphires, and these contents were speculated to be added artificially intending to colour alteration.
Having confirmed with clients, most of the stones were purchased from brokers in Bangkok. They were not sold in particular low price and they could be returned to the seller. Some pieces were purchased last September, but most of them were obtained this year.